1. Field of the Invention
The present invention relates to a plasma exhaust gas treatment device that is capable of removing exhaust gas components in exhaust gas, which is exhausted from an internal combustion engine, with the minimum electric power consumption.
2. Description of Related Art
A variety of catalyst devices have been developed to remove harmful exhaust gas components included in exhaust gas exhausted from an internal combustion engine of a vehicle. A variety of catalyst devices are known. For example, a plasma exhaust gas treatment device, which treats exhaust gas by corona-discharging (plasma), is known as a device for removing nitrogen oxide (NOx) among the harmful components (Japanese Patent Provisional Publication No. 5-59934).
This plasma exhaust gas treatment device supplies power to a discharge tube, which is provided in an exhaust passage, to bring the exhaust gas into a plasma state, and decomposes the NOx in the exhaust gas into nitrogen and oxygen as harmless components. This conventional plasma exhaust gas treatment device controls the power supply according to signals indicating the quantity of gas and the concentration of NOx at an inlet of the discharge tube to thereby supply high power only when a load is high without supplying unnecessary power when the load is low. Consequently, the exhaust gas is purified according to the variations in the load of the engine.
If, however, a vehicle is used under broad driving conditions from a low speed to a high speed or from a low load to a high load; there is a substantial variation in not only the discharge of the exhaust gas but also the quantities or concentrations of various harmful components in the exhaust gas. The exhaust gas includes harmful components such as NOx, hydrocarbon (HC), carbon oxide (CO), sulfur oxide, nitrogen carbide and sulfur carbide.
The power consumption decomposed by the plasma exhaust gas treatment device differs according to the kinds of the harmful components. Therefore, the conventional plasma generating device cannot sufficiently purify the exhaust gas including a plurality of harmful components.
It is therefore an object of the present invention to provide a plasma exhaust gas treatment device that is capable of purifying a plurality of exhaust gas components included in exhaust gas from an internal combustion engine with a small power consumption.
The above object can be accomplished by providing a plasma exhaust gas treatment device comprising: a plasma generating device provided in an exhaust passage of an internal combustion engine, the plasma generating device being supplied with power to generate plasma and purify exhaust gas components; power supply control means for controlling power supplied to the plasma generating device; wherein the power supply control means having exhaust gas condition sensing means for sensing and estimating the quantities or concentrations of plural exhaust gas components included in exhaust gas exhausted from the internal combustion engine; and the power supply control means finds power conditions required to purify each of the plural exhaust gas components sensed by the exhaust gas condition sensing means and determines power to be supplied to the plasma generating device according to the power conditions. Thus, the plural exhaust gas components are removed with a small power according to the driving conditions. The power supply control means can provide the plasma generating device with the power conforming to the maximum power condition among the power conditions found for the plural exhaust gas components.
More specifically, the power condition required for the plasma generating device to purify the exhaust gas is that power for acquiring the maximum energy consumption among the energy consumptions required for the plasma generating device to purify plural kinds of exhaust gas components is found and the found power is then supplied to the plasma generating device.
The plasma exhaust gas treatment device of the present invention can remove plural kinds of exhaust gas components, which vary according to the operating state of the engine, with a small power consumption. It is therefore possible to efficiently purify plural kinds of exhaust gas components while reducing the deterioration in fuel economy regardless of the quantity and conditions of the exhaust gas.
In another preferred mode of the plasma exhaust gas treatment device according to the present invention, the power supply control means has power condition calculating means for finding a power condition required for the plasma generating device to purify each of the plural exhaust gas components sensed by the exhaust gas condition sensing means to a predetermined reference value or less; and the power supply control means provides the plasma generating device with power according to a maximum power condition among the power conditions found by the power condition calculating means with respect to the plural exhaust gas components.
This plasma exhaust gas treatment device finds the power required for acquiring the maximum energy consumption among energy consumptions required for purifying a plurality of exhaust gas components to predetermined values or less, and supplies the found power to the plasma generator to thereby remove the plurality of exhaust gas components, which varies according to the operating state of the engine, to a predetermined reference value or less with the minimum power consumption.
In yet another preferred mode of the plasma exhaust gas treatment device according to the present invention, the exhaust gas condition sensing means has plural exhaust gas maps representing the quantity or concentrations of plural exhaust gas components found in advance according to an operating state of the internal combustion engine.
In yet another preferred mode of the plasma exhaust gas treatment device according to the present invention, the exhaust gas condition sensing means has a sensor for sensing the quantities or concentrations of the plural exhaust gas components.
According to this preferred mode, the exhaust gas condition sensing means may use an instantaneous value of the quantities or concentrations of the plural exhaust gas components sensed by the sensor, or may use a sensed sum value or an average sensed value of the quantities or concentrations of the plural exhaust gas components sensed by the sensor in a predetermined period of time.